If you are in Canada at the time you apply, you have two choices of application, inland and outland. See here:
http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-how.asp#step1The first link that says "If your spouse, partner or accompanying dependent child lives with you in Canada" is referred to as inland and the 2nd link that says "If your spouse, partner or dependent child lives abroad" is referred to as outland.
The difference in how they are handled is huge.
If you go with inland, you would send your application to Vegreville and it would be processed there until first stage approval which takes 5-6 months. You could apply for a work permit and a visit visa extension at the same time and they will not actually kick you out of Canada while they are processing you but it is not advised for you to leave either since if you can't get back in, your application is gone. Another huge drawback is that if they want an interview, they will forward it to your local CIC office where you live without the first stage approval. That means no work permit and no health care. The local CIC office will do the interview but some of them are so busy you can be waiting for this interview up to 3 years. That means stuck in Canada with no work permit and no healthcare for up to 3 years. That is obviously not a very good thing. Normally though, you would have your work permit at first stage approval in 5-6 months and your PR in 1-2 years.
If you go with outland and I would rather recommend that, you can still give a mailing address in Canada but say you want your application processed in the UK, it would be sent to Mississauga and takes right now 43 days to process the sponsor part, see
http://www.cic.gc.ca/english/information/times/canada/process-in.asp#sponsorship , that is where they make sure that your wife doesn't have a criminal record and hasn't been on welfare. After that your file goes to London and takes on average 4 months, see
http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp#europe and then you get your PR. If London wants an interview, you would have to go there, that's the only drawback. For outland there is no work permit. You can apply to extend your visit visa when it's about to expire but your application will be close to finish processing by then.