Hey,
you can get married anywhere you want =)) even on a cruise ship.
and you will be able to sponsor your girlfriend afterward, however you should check why she was denied the visitor visa to Canada, so you can write a cover letter for your application explaining all that.
The processing time depends on the office you will be dealing with (CIC website has all the timelines),. You have to however note, that it can be longer that what they estimate.
Cheers, Raccoon