Yep, being able to extend your visitor status has nothing to do with whether or not you initially needed a TRV to enter. You can apply online OR by mail (paper). Most say it's actually better to apply by mail, because: 1) you retain physical proof of having sent it in, eg. courier or mail receipt with tracking number, and 2) it takes them a LOT longer to get through mail-in applications, which means you get to be on implied status much longer while waiting. See here: http://www.cic.gc.ca/english/visit/extend-stay.asp.
There are probably thousands of posts on this board now about how to extend status while waiting for PR, but the gist of it is that the best thing to do would be to state the reason for extending as wanting to wait out the PR process with your spouse/sponsor, and then include proof of being sponsored (marriage certificate, copy of PR fees receipt, immigration file number and visa office name, etc), along with proof of being able to afford to stay that long without work (copies of bank statements from one or both of you, signed statement from you saying he won't have to work because you'll support him if needed [if that applies], etc). Plus a copy of the stamp in his passport to prove when he entered and all that fun stuff.
I'm sure others on here can help you better than that, if you guys do end up having to extend his status. But yes, definitely, he doesn't need an actual TRV to do so.
