I think that your best choices would be the Kobo or a Kindle; I would suggest the Sony devices as well, but you have specified that you would like wi-fi, and the only Sony model that is sold with wi-fi is the PRS-950, which is only sold in the U.S. Between the Kobo and the Kindle I would personally choose the Kobo, as I like the touch screen, it looks like it might be able to render PDFs better than the Kindle and the Kobo store seems to be better for Canadian content (judging from the books that I've searched for there, anyway). If wi-fi isn't a must for you, I would say go for the Sony - you can shop at the Kobo store, and you have certain bonuses such as built-in multilingual dictionaries and reflow for PDFs, as well as rtf support. I also like the metal build of the Sonys, and the file organization abilities that it has ("collections").
I use my Sony for novels and some technical PDFs, but I find that PDFs display better on a larger screen, so I use my iPad for PDF reading when I am at home.