I dealt with Alberta Diamond exchange, great experience with them as they were knowledgeable and were very patient in asking thousands of questions.
Blue Nile was also very good with the customer service and the available cuts and styles. However, they don't have Canadian diamonds, and that was a deal breaker for her
Ultimately, because my girlfriend is very into sustainability and the environment, I got the diamond from Brilliant Earth (
http://www.brilliantearth.com/), an online environmentally certified diamond company that specializes in Canadian diamonds. We only got the loose diamond from them since they didn't have a ring that she liked, and I wanted a local jeweller so that she could always get her ring cleaned
I'll report back in 2 weeks when the ring and diamond are put together