It will be cold in October and November (Toronto is colder than Vancouver). I went last year with my daughter and grand daughter of 15 months and we stayed for 2 months.
It's better to bring along all the medicines that might be useful. Because they are very expensive. You have to buy the medical insurance as well. If you know some agents in Canada, they will give you discount up to 40%. You can ask for diappers and can food for baby on the plane. Bring some small toys since the journey takes hours so that the kids won't be so boring. Also bring along bottles of water for baby because you are not sure whether the water they supply is suitable for babies.
We didn't bring much clothes with us. In Canada you can easily buy some clothes with big sale. Sometimes they are even cheaper than HK and the quality is very good. The Pampers you buy in Canada is so much better than HK, it smells of babies(good smell). We brought home 6 big boxes (of course with discount). They also have Cruisers for toddlers which we can't get in Macao. I don't know whether you can get it in HK.
I hope this information could help.
PS. Don't forget to bring along thick coats for the kids. Because when you leave the airport in Canada you will feel very cold specially the sudden change of the temperature.