You can visit, but if you're intending to stay in Canada with your sponsor, you're better off having him/her accompany you on your entry to Canada. If you are truly coming just for a short time, have proof of return itinerary and proof of your ties to the US (job, home, etc). And try not to have to mention that you have a partner in Canada and a PR ap in process. BTW - most IOs at the US/Canada border are not going to buy an "exploration trip to have an idea about Canada".