As for Canada, York Soaring Association will take short term members. As an (I presume) American, you will need a reciprocal licence, and a medical, but this can be a category 4 (self declared). You can find info on the club at
www.yorksoaring.com.
York has on-field accomodation, and a DG 500 a K-21 and 3 Grobs in its fleet, and also offers aerobatic instruction. It is about 60 miles from the Toronto Airport (YYZ).
Also, is it possible to join clubs for a week or two? Any options in Canada?
Thanks ... Aaron