While it is not the requirement for TRV to get medical insurance, it sure does make your case stronger (still no guarantees though).
Besides, bringing your spouse on TRV to Canada without any medical coverage does put you and spouse at risk. You may be saving a few hundred dollars in insurance, but God forbid if medical care is needed during that peiod, you are looking at spending thousands.
When I had applied for my wife's TRV last year, I bought travel insurance from Ontario Blue Cross. Cost was about $75-$90/month with no prior health conditions. The TRV was approved and I had the peace of mind when she was here.