You can get married wherever you want. As long as it's a valid, legal marriage, CIC will accept it.
If you have been admitted into the UK for at least 1 year, then you can have your application for PR processed in London. Otherwise it will be processed in Islamabad - you don't actually have to be present in Pakistan while it's being processed, but if an interview is required, you will have to go there for it.
Because your wife is a Canadian PR, she will have to be in Canada while sponsoring you, she can't be living somewhere else in the world. Citizens can sponsor while living abroad, but PRs can only sponsor if they are living in Canada.
thanks for ur reply
little bit confusion in uk stay
well i m living in uk since last 5 years , right now i have 11 month visa left which m gona extend near expiry as usuall , so u mean i have 2 apply from islamabad not from london ?
plz correct me if m wrong
thanks once again for reply