Would 1 hour 10 minutes be doable to make the connection? Same airline, if that matters. Would have luggage.

"<Same airline, if that matters>"

Same airline matters, more importantly - on one and same same ticket? If yes, then the airline considers this connection time sufficient, and if they get you to Montreal late, they are obliged to put you on the next available flight.

If that "next available" flight is not anytime soon, you'd better know what other airlines have onward flights to DEN and insist that you be booked on one of them, so do your homework ahead of time.

I don't have the rules at my fingertips, but it will be a good idea for you to look them up and have a printout or have them on your phone, together with flights by alternative airlines that you can ask to be booked on if worse comes to worst.

Know your rights and be able to document them when time is of the essence.

Thanks Michel, that was my other question, what are they obliged to do. Yes, same ticket. Where are rules on this?

If you scan down far enough you'll find the "arriving from international/depart for US" process:

http://www.admtl.com/en/guide/connec...#International

I'll bet that you'll find more on www.flyertalk.com, those folks go to the nth degree in knowing the ins and outs

Also see https://www.smartertravel.com/2016/0...ghts-go-guide/

You may know this but the minimum connection time for international arrivals through to the US at YUL is 70 minutes. At least it is for Air Canada:

http://www.aircanada.com/en/travelin...html#faq:6-5-*

You may have to go through US border entry procedures in Montreal under the preclearance system administered by the US. https://www.cbp.gov/border-security/...s/preclearance
I live in Canada so haven't done it myself but it appears US-bound passengers are directed into a separate line-up than those of us entering Canada. I certainly don't know how fast that line-up moves but regard an hour as a tight connection, especially since your plane is flying west into the trans-Atlantic winds.