Retraction before nasals

Questions about "Regional variation in Canadian English vowel backing" by Erin Hall*
Erin Hall says that /æ/ is retracted before nasals in Vancouver. In fact the overall retraction of /æ/ before nasals was 100% in all the speakers from Vancouver in reading from a word listt and in causual speech. (and 75% from reading a passage). (Compared to 0% in Toronto). Is this retraction the same as the Canadian shift? Or is this something different? Is it true that before nasals it's retracted more often than in any other environment? Is it true that it's a marker of West Coast English and is found 0% in Toronto? Is it realized as [æ] in Toronto, or is it diphthongized? Does this mean that it is never raised and diphothongized in the West Coast?

*Available here: http://r1.chass.utoronto.ca/twpl/pdfs/twpl18/TWPL18_Hall.pdf

OK, this does not address your questions, but I just started reading the article you reference, and on the very first page I found the following:

"Although no other studies have examined this particular variable as it pertains to an East-West regional difference in Canadian English, vowel retraction has been noted in other dialects of English, particularly the Southern England English (SEE) variety as described by
Chambers (1992). In SEE speech, the vowel /æ/ is retracted before anterior voiceless fricatives in words such as plaster, bath, laughing, and class, and before clusters of /n/ + obstruent, as in dancing, branch, and candy"

The only relevant example in that list would be "candy". All the others do not have /{/ in RP (which is most likely what's meant by SEE) but /A:/.

>> (where raising/diphthonging is usual in CanEng) <<

How much raising/diphthongizing is usual? Is it like how NCVS speakers pronounce /æ/? I find that extremely noticible. In my own speech (I'm from the Western US), I've noticed that if I do raise and diphthongize before /n,m/ it is very slight--because until I read about this phenomenon I thought my /æ/ before nasals was about the same as any other environment, (except for /g/, where I identified the "a" in bag as the same vowel as in "beg", and I didn't know that "bag" was supposed to have /æ/ in it.)

>> I think this article is referring to the use of an unraised or diphthongized TRAP vowel before nasals (where raising/diphthonging is usual in CanEng) <<

But the article clearly states: "For each of the test words, the vowel was recorded as either [æ] or [a]..."

Following nasals motivate vowel shifts in Western American English:
http://www.ling.upenn.edu/NWAV/abstracts/nwav36_baker.pdf

>> From "Following nasals motivate vowel shifts in Western American English":

>> The vowel in hang has merged with long-a (the vowel in Hague) <<

Yes, it certainly has.

>> The vowel in ring is also raised and fronted, merging with long-e for some speakers. <<

I've heard (some) Californians do this. I don't. "Will you 'seeng' a song?" <<