Hello you Canadians
I grow mainly midseason heirlooms here in Zone 3A just outside of Edmonton. Mine do quite well and I grow only a few earlies to tide me over unitl the biggies start to ripen, (about now for me) . I do avoid late varieties for the most part although I am still tempted by a few here and there. Have a look specifically at some Russian and Ukrainian heirlooms from Tatiana's Tomatobase for hundreds of great varieties. I find the Russian, Ukrainian and Slovanian tomatoes like my short season Canadian garden. Tatiana's is a Canadian company based in B.C.
http://t.tatianastomatobase.com:88/wiki/Main_Page amazing amount of information there as well as an extensive catalog of heritage seeds, not only tomatoes.
Karen O