As a Canadian who lived several years of his life just outside of Boston, and having several American friends and acquaintances, I have encountered on many an occasion the stereotype/cliché that Canadians say things like "hoose" and "oot".
In fact, that is not quite an accurate description of the unique pronunciation that many Canadians use for this diphthong. The whole effect, a fascinating phonological process, is known as Canadian Raising.
The process is phonologically-conditioned; that is to say, the variants depend on the phonological environment of the sound. In the case of Canadian raising, it depends on the voicing of the following sound... whether the sound is voiced (articulated with vibrations in the vocal cords, eg. z, d, b) or voiceless (artculated with no such vibrations, eg. s, t, p). When followed by a voiced sound, the "ou" diphthong will be pronounced by most Canadians in just the same way that most Americans would. (A rough phonetic symbol representation: /aw/. This represents, more or less, an "ahh" sound pronounced with the lips rounded, as though pronouncing the letter "w".) So, in many dialects of both Canadian and American English, the word "loud" would sound more or less identical.
When followed by a voiceless sound, however, in most varieties of Canadian English, the "ou" sound changes slightly. (Another very rough phonetic symbol representation: /^w/, where ^ represents the "u" sound in "but", "plus", etc. In other words, this diphthong is articulated with said "u" sound combined with the lip rounding of "w".) So, for most Canadians, word pairs such as "lout" and "loud" would show an example of this slight pronunciation change, whereas many Americans would pronounce such pairs with the same diphthong.
Interestingly enough, this phenomenon is not strictly a Canadian thing... a similar process occurs throughout (throughoot?) Canada and the Northern United States with the sound "aye". The phonological environment is identical; before voiced sounds, the sound is /ay/ (an "ahhh" sound articulated with a closely follwing "ee" sound), while before voiceless sounds, it becomes /^y/ (the "u" sound of "plus" with a closely following "ee" sound), giving word pairs with similar pronunciation differences, like "wife" versus "wives", etc.
As stated, this occurs in many dialects of the Northern USA... in some Southern dialects, the case gets even weirder, with the sounds in such words not being "real" diphthongs at all. For example, instead of /ay/ in "wife", the diphthong becomes an "elongated" "ahhh" sound (phonetic symbol: /a:/), leading to pronunciations like "waahhf" for "wife".