There will be plenty of foliage wherever you go. The Eastern Townships are beautiful, places like Bromont, Sutton, Magog, Orford, etc will probably be at peak. This area has ski resorts, wineries, cideries, lakes and some of the best road bike trails anywhere.

Thanks for the information. Are there any mountains in driving distance of Montereal that would have fall foliage? Are there any good routes around the St. Lawrence River? We have not driven in this area of Canada before. What would be the best routes to the Eastern Townships? Are there cruises on the St. Lawrence River you would recommend?

Thanks for any suggestions!

The areas I described are due east of Montreal, just off route 10, very easy driving. Bromont, which is a ski town at the base of a mountain, is less than an hour from Montreal. Another 1/2 hour gets you to Magog is a very scenic lakeside resort town with plenty of mountain scenery. Mt Orford Park is just a few miles from Magog. There is a very picturesque abbey - St. Benoit-du_Lac, situated on the lake just a short drive from Magog.
Of course you could also head north from Montreal into the Laurentians, which I'm not familiar with.
As for cruises on the St. Laurent, there are sightseeing boats in the Old Port of Montreal, but the river is fairly industrial near the city. I don't know about boat rides other places on the river. There is a fair amount of parkland on the island of Montreal along the river however, with plenty of foliage viewing. Also, there are lot of other parks throughout the city with magnificent maples that should be at their peak.
The bonjourquebec.com website has lots of information.

Thanks! This is great information we can certainly use.

Can anyone give us information about visiting the Laurentians? Is October a good time to visit there--fall foliage, etc.?

You wanted some info on the Laurentians. These are not high mountains so are wonderful, meandering country roads. If you travel Northwest of Montreal you can come across some beautiful picturesque fall landscapes. Depending how much time you have, head towards Mt.Tremblant passing through St. Jerome, 30 minutes, St. Sauvuer-de-Mont, 63km/39miles from Montreal. St.Sauveur is a quaint little town, full of small restaurants and art galleries along the main street. My favourite place to eat Sunday breakfast/brunch there is Breton Crepes set in an older typical Quebec style house. I guarantee you've never had crepes like these before. Go on an empty stomach! Mt.Tremblant, about another 100km/62mile,is a downhill ski centre but open all year round as an outdoor tourist destination. There is a wildlife park there as well. Depending on what type of place you want to stay at you could overnight there. There is a lot variety of accomodation from luxury in the ski village (kind of like Vale or Whistler) to cabins, B&Bs etc.

As to when to visit: this of course depends on the year and weather of course. Since the Laurentians are higher up and cooler that will make a difference as well. Late September to early October may be safer than mid October for the best colour. All it takes is several frost and rain/windy days and the leaves will be gone. Mt. Tremblant is known for its windy peaks.

Hope this helps. It's a very beautiful drive so give yourself time to stop enroute to enjoy.

Sorry, I mispoke, Mt. Tremblant is 100km(62 miles) from Montreal...I really should preview before I send.

Agree with MsLizzy, the towns you go through along the way to Tremblant plus St Jovite ( now part of Mt Tremblant)are a beautiful part of Quebec. Many artisan food places and shops.
St Jovite ( town nearest to the mountain) is full of artsy stores and restaurants. Tremblant village has a ton of places to stay.
We enjoyed:http://www.tremblant.ca/reservations/en/Mont-Tremblant--Hotels--Condos-Homes-in-the-Pedestrian-Village/mg_50/v_1804/Le-Lodge-de-la-Montagne-Les-Suites-Tremblant.detail