If living in Montreal, it would be ideal to know some French but not make or break. In most places as long as you put in effort to learn and try to communicate in the local language, people tend to appreciate that - and being surrounded by the language will certainly help you to learn quickly.
An international school would probably be the best option but they are usually very expensive. It's worth noting, though, that public schools in Montreal do provide support to non-French speakers, but it will probably still be a bit of a struggle. More info on the Expat Arrivals Schools and Education in Montreal page.
The school system in Toronto is a bit more advanced, and language barriers will be much less of a problem in general in Toronto. Again, more info can be found on the Schools and Education in Toronto page.
We also have Cost of Living in Montreal and Cost of Living in Toronto pages, which you can use to compare that aspect of life.
There's some information on the job market on our Working in Canada page. Both Toronto and Montreal also have "Working In" pages which you can navigate to using the bar on the left-hand side of the webpage.
Best of luck!