During the year, you will in fact have taxes deducted as appropriate where you work, Ontario in this case.
However, at the end of the year, you will file tax returns as a Quebec resident. That means filing both a Federal and a Provincial return(revenue Canada and Revenue Quebec). You get credits towards your Quebec taxes on your federal return, so what usually happens is that you end up with a big refund from Canada, and bill owing for Quebec.
I reside and work in Ottawa, so I only have 1 income tax to file before April 30 of each year.
Some people think that residing in Gatineau (cheap day care, cheap rent, minimum wage 10.35$...) and working in Ottawa (minimum wage 11$) is very helpful, but it's not since you'll be filing federal and provincial taxes.
with 2 incomes it might be helpful yes.
As for the benefits, I won't rely much on the healthcare system in Quebec. do some research and you'll see why.
Ontario(especially Ottawa) has the best healthcare system at the General Hospital and the CHEO.
Ottawa has its pros and cons. for a family it is a amazing but for jobs it's a bit tough market since all the government is located here, and you need to be a Canadian citizen for at least 10 years to work in gvt jobs.
Good luck!