During summer, Montréal Belleville is easily doable in an SR+. But beware during cold weather, you won’t be able to skip Cornwall (unless you have a 2021 with heat pump maybe).
Did this trip before in my 2019 SR+, both + 20C and -20C, and never had to wait at any charger for empty spot. In those cases I didn’t find any of them to be a problem even if it far from the highway like Cornwall. We’re talking 2-4 mins extra here, not a big deal for me. That being said, I prefer Belleville because there are more restaurants nearby and I usually make it my lunch stop.
Funny enough, I did the Montréal -> Toronto -> Montréal road a week ago (sept 1 and 3) and got a totally different experience. I feel that I need to update this answer.
First of all, I realized now that when I said "Montréal Belleville" is doable in an SR+, what I really meant was "Kingston -> Montréal", or "Cornwall -> Belleville" as I've done both in 2019 (confirmed by my Supercharging history).
So last week, when I left Montréal with 100% SOC, the car said it
couldn't make it strait to Kingston. Weird enough, as I did Kingston -> Pointe Claire in 2019 . But ok, might be something related to different weather, battery degradation or going "down" the st-Lawrence I guess ? Next,
the car showed Cornwall as closed. The car navigation actually routed me to the Casselman Supercharger,
then back to Kingston using some rural routes between the 417 and 401. Quite the detour...
On the way back, fortunately
Cornwall was up and running again. But after supercharging in Kingston (up to around 88%), the car navigation still insisted I stop by Cornwall, which I found strange as I managed to skip it in 2019. The navigation said if I was to skip Cornwall, I would have gotten home at exactly 0% SOC. I think what happened in 2019 is I charged close to 100% SOC to avoid Cornwall. This time (2021), If I would have charged around 95% SOC at Kingston, I would have make it... maybe. For some other reason, the car navigation wanted me to charge 15-20 mins at Cornwall so I would get to my destination (in Montréal) at 20% SOC (I waited 5 mins less than that and got home at ~14% SOC thank you). So I don't know if the navigation would have let me skip Cornwall and arrive below 10% even if I got a full charge at Kingston...
Finally, compared to my 2019 and 2020 trips, there was some waiting involved at Kingston in 2021. On the first day,
Two stalls were not working, and a third didn't seams to charge when I plugged in (but a Model Y managed to charge on it later on). In the end, I waited no longer than 20 mins to plug in, plus everyone at the Supercharger was super friendly, which made everything fun. On the way back, I couldn't skip Kingston as I made a detour between Belleville and Kingston. The non functioning stalls at Kingston were running,
but where giving a mere 20 kW. I still used them, as they were the only one available and I didn't mind the wait (wasn't too low and took the time to go eat). And again, met a bunch of friendly people at the Supercharger.
So long story short,
Montréal -> Kingston a big no-no in an SR+, but
Kingston -> Montréal is doable
if you charge up to 95% at Kingston. But in any case, I still prefer skipping Kingston (and doing Cornwall -> Belleville) when I can.
Oh and Brockville can't come soon enough.