This page is about the technical details of Canadian Accents. It is very technical, going into a high level of linguistic detail.
Canadian raising is a phenomenon which raises the nucleus of the diphthong in words that have /aI/ /aU/ followed by voiceless consonants (e.g. p, t, k, f, s, and the "th" sound as in "thick"). This feature is quite widespread in Canada. It is receding in parts of British Columbia. There are some regions in the US which also have it. In the US, the raising of /aI/, the vowel sound found in words such as "rice", or the letter "I", is quite common and thus is unremarkable. However, the raising of /aU/ (found in common words such as "out" or "about") is much less common, although it is found in some areas of the US near the border. People that do not possess this feature in their dialect often think that people with it say "ote" or "oot" for "out", however a more accurate representation of it would be the "uh" in "huh" followed by the "oo" in moon. So people without the raising pronounce "out" with the same diphthong as in "pow", but people with it pronounce it more like "uhoot". In some areas it is pronounced more like the "e" in "red" followed by the "oo" in moon. An excellent demonstration of Canadian raising can be found here.
The Canadian shift is a vowel shift, which is also found in the Western US (areas west of North Dakota), but it is less widespread in the Western US, and contains the same features as the first stages of the closely related California vowel shift. The shift is led by young women. Male speakers tend to have it to a lesser extent. It shifts many vowels in the opposite direction of those found in areas of the US affected by the Northern cities vowel shift (found in such cities as Chicago and Detroit.) Thus the accent changes immediately by crossing the border from Detroit, MI to Windsor, ON—and thus someone from Windsor has a phonology closer to someone from California even though it is thousands of miles away than that of NCVS affected areas just across the border. It is caused by the merger of the vowels in words such as "cot" and "caught" (Don, Dawn; hottie, haughty, &c.) which causes an unstable vowel system. Thus the vowel in "cot" and "caught" both shift to the position occupied by "caught" (e.g. how a speaker with a conservative accent from the Midwestern US would pronounce "caught"). This is very noticeable to speakers who do not normally merge the vowels—as there are many places in the US that have vowel configurations that are resistant to the cot-caught merger—such as the Inland Northern area. The next stage in the shift causes the vowel in "cat" to shift. It is pronounced with a low central vowel. This is the opposite of what happens in the Northern cities vowel shift. Thus an advanced speaker from Canada would pronounce the word "map" the same way someone with the NCVS would pronounce "mop". The CVS then shifts the "e" in "met" to the "a" in "mat"—how "mat" was pronounced before the shift. However "met" and "mat" are still quite distinct—since the vowel in "mat" also changes, the two words are not confused. The last stage of the shift, shifts "i" to "e" (e.g. mitt to met). Most speakers who have the shift are completely oblivious to it (as they have nothing to compare their vowels to), and do not even notice it in others. Most speakers do not have it consistently, and have only the first few steps of the shift. However, many speakers with the shift notice those with the Northern cities vowel shift (e.g. many Canadians can recognize the accent in Detroit because the vowels are moving in the opposite direction—for example, the "a" in "mat" is raised and diphonized to "ee-uh".) Many speakers from the parts of the Northern US that have the NCVS can likewise detect a Canadian accent on the basis Canadian shift alone, however people from the Western US, especially areas affected by the California vowel shift cannot detect a Canadian accent solely based on the Canadian shift.
There are some other features that are found in Canadian English but not as widespread in the US, especially in areas far from the border. The first is the treatment of pre-rhotic consonants. Most speakers in Canada would pronounce "sorry and "tomorrow" with the same vowel as in "ore", but for example someone in California would be more likely to pronounce them both with the same vowel sound as in "are" (however pronounce other words such as "horrible" and "Florida" with "ore"). However, in other areas, such as the Pacific Northwest, some speakers pronounce both with "or", or both with "are", or even "sorry" with "are", and tomorrow with "or". The same is true of the Upper Midwest. Many define "General American" (an vaguely defined neutral sounding American accent), as having most words, such as "Florida" or "horrible" with "ore", but "sorry" and sometimes "tomorrow" with "are".
A high percentage of Canadians than Americans use the vowel in "mat" rather than "mop" to pronounce the "a" in foreign loan words such as "pasta". A higher percentage of Candians than Americans pronounce "shone" to rhyme with "shawn" (the cot-caught merged vowel, which depending on the speaker and situation can be anywhere between the conservative (non-merged) pronunciations of "cot" and "caught") rather than "drone".
The accent found in Western and Central Canada is fairly homogenous, especially the inland area (not including Vancouver and Toronto—which both have a more variable pattern—e.g. more variation between individual speakers). The merger of the vowels in cot-caught is extremely widespread, and only a small percentage lack it. Canadian raising is also very common, although receding in some parts of British Columbia. The Prairies generally have the strongest Candian raising. Most people that possess Canadian raising (on both sides of the border) are unaware that they have it, and cannot hear (without practice) the difference between their pronounciation and that of speakers that lack it. Raising of /aI/ usually goes unnoticed by speakers that lack it. However, some speakers that raise /aI/ can hear the difference between "rider" and "writer", even though as in all North American dialects the "t" is realized as an "alveolar flap" (sounds like a "d" to most people), because the nucleus of the diphthong starts on a different vowel: ah+ee vs. uh+ee. The raising of /aU/ is much more noticeable, and Americans that have this feature are often mistaken for Canadians by other Americans when they travel to other regions, regardless of how the rest of their vowel system is configured.