My wife and I were in the same situation Maggie.
She visited from the UK 4 times before we married.
Concerning what to say for the visa, here's what we did.
Although British citizens don't require visas per se, immigration at the airport usually asks a few questions.
On the first two trips, my then girlfriend said she was travelling to see friends, and staying with me.
This was truthful.
On the 3rd trip, she said she was coming to see and stay with her boyfriend. She had a return ticket.
On the fourth trip, she said she was coming to see her boyfriend, but when questioned why she didn't have a
return ticket, answered honestly that she may have to return to the UK at any time for business/family matters.
Again, this was true. The officer made sure to stamp her passport, and write in a 6 month leave date.
We managed to get her divorce and settlement done while she was here on 6 months visa exempt status,
and we decided to marry in a civil ceremony in Ontario. The marriage certificate took only 8 weeks as we
wrote a cover letter asking to expedite it if possible explaining the immigration situation. It would have arrived
sooner had they not mailed it to the wrong address. Our MPP helped with this!!
We then applied to extend her temp status, stating that a sponsorship/PR application was in the works.
Here we sit. Waiting like everybody else, fingers crossed.
I will keep you aware of our progress.
Good luck.