Asak,
Though my VO is New Delhi, Im a frequent visitor of the Pakistan thread and have some idea how things work with CHC-Islamabad. I would strongly recommend that you do not have a Nikah over the phone, and that you have your Nikah, Valima, Rukhsati, the works. done all at one time when you visit Pakistan. Moreover, it does not take much time to register your marriage and get a marriage certificate. So getting the paperwork ready is not really a problem.
Make sure you are already collecting all kinds of proof from now itself. Phone records, chat records, emails, facebook evidences, gifts exchanged etc. You seem proactive in your approach, so I suppose you are doing all of that right now. In case you arent, I suggest you get down to business

Simple, open and shut cases take easily upto 16-18 months, so you might not want to squeeze in a Nikah-over-phone in the middle of it all and complicate things for yourself.
I also suggest you read through these threads to get an idea of the whole thing. It has people who applied to CHC-ISB.
http://www.canadavisa.com/canada-immigration-discussion-board/chc-islamabad-spouse-sponsorship-timeline-2009-2010-t28775.43275.htmlhttp://www.canadavisa.com/canada-immigration-discussion-board/chc-islamabad-spouse-sponsorship-timeline-2011-2012-t63735.2370.htmlHope this helps. All the best!

Shamsia.