Exactly. If this was an Ipsos-Reid poll, I'd have a lot more faith in them. However, the Gay and Wail strategically avoided them to manipulate the result.
This is the latest Ipsos poll I could find on the issue: December 2004. From this poll it look like about 40% are totally in favor of gay marriage, about 30% totally against, and the rest wishy-washy. If you assume that half the wishy-washies break in either direction when it comes to the new law, you end up with the 55% found in the Globe and Mail poll.