Trying to apply for a visit visa with a Canadian spouse is hard because they will not believe that he is planning on leaving you and going back to Mexico again when his visit visa expires. You can still try it but the reason they imposed visas on Mexico this summer was because they were having a lot of problems with Mexicans coming to Canada and overstaying. You can try applying for a visit visa for him but be prepared that you may get denied.
Another thing you can do, you can start an outland sponsorship, make sure you have a bulletproof application and hope it's fast. Once you have been approved as a sponsor which takes about 7 weeks, you can apply for his visit visa. Then at least you will have shown that you have passed the requirements to sponsor him so maybe they will let him visit although he would still need to prove that he will return to Mexico when his visa expires unless he gets his PR first. Another thing with outland is that if there are questions about the application, he would be called for an interview in Mexico so he would have to go there so another reason why he might be less likely to overstay.
You can also go back to Mexico to be with him, have your baby there and sponsor him for PR while you are living in Mexico and only move when he gets it.