TD does have 4 ATMs in Southern Ontario that do dispense US$ cash. These can be convenient after-hours if you need cash late at night or during a holiday, or want to avoid bank lineups. I assume you can withdraw from your Canadian dollar TD account with their usual commissions. I would also think that non-TD customers could use them, at TD's regular commissions and ATM fees.

TD ATMs that give out US$ Cash:

Click the link to open up a map in a new window

3930 Montrose Rd., Niagara Falls    
3281 Dougal Ave., Windsor
2110 Wyandotte St., Windsor
55 King St. W., Downtown Toronto

Too bad they don't have more locations with them, but at least they're located in border areas. Note that the downtown Toronto one is actually in TD centre in the concourse I believe, I'm not exactly sure, so you might have to do some searching.

I'm not sure if it is possible to withdraw from one's US$ account at these ATMs, I'd imagine it's possible if you have a TD US$ account, but not sure about other bank's US$ accounts.

Other Canadian Banks with US$ ATMs

Some other banks do have these US$ dispensing ATMs in Canada too, and I'm trying to get a listing of them, but I haven't received any responses yet.

Also, Scotiabank is a member of the Global ATM Alliance, so they can actually use Bank of America ATMs at some reduced (or even zero) fee. Best to talk to your banker about that one.  No other Canadian or US Bank is a part of this alliance.