AFAIK Caisse is going to be charging ARTM a fee per of 55 to 72 cents per km per passenger (exact rate changes depending on ridership). They are not directly involved in setting the fares the end users will pay.
I'm not aware of any announced changes to STMs existing fares for end users, but at 72 cents per km the government would receive a bill of ~$2.20 for the trip you describe.
Oh my! This sounds like another 407 travesty!
Boy is the crap going to hit the fan when people figure this out - unless the province is going to be paying huge subsidies. Looks like Montreal and/or taxpayers have been very screwed!
Currently that trip (Zone 1) would cost $3.25 (using tickets), including transfers to bus and metro (which is 45¢ higher than the $2.80 bus/metro ticket). With a monthly pass, Zone 1 fares on that line are currently only $13 a month in addition to the $85 monthly pass.
That'd be a very short trip as well; Zone 1 covers that line out to Montpellier station on Cote Vertu. The entire portion of that line on the island (and the old CP line to the Point-Claire/Beaconsfield border) is in Zone 2, which is only $3.79 ticket or (including bus/metro).
Simply on it's own, the subsidy might make sense ... but if they use current STM fares, or even RTM fares, and a lot of people transfer to the Metro, it will be interesting to see how the cash flows work. Especially given the projected ridership, which at 190,000 a day - about 57 million a year, is similar to the entire GO Train network.
The commuter rider from, say Bois-Franc travels about 12 km each way to Central Station. So that's (assume 55¢ per km) a payment to the caisse of $6.60 a trip. If you do 40 trips a month (20 working days) that's $167 a month. But a monthly pass for just (and the entire Zone 1 RTM rail network) is only $97 - and only $114 if you include bus and metro.
So the government is going to subsidize $180 per rider per month? Presumably more for riders who are doing longer distances!