Moving freight to trains only makes sense when it's not time sensitive, but because many companies don't want to warehouse product anymore (instead having just enough arrive just in time) trains don't work for the overwhelming majority of freight.
For example, I have on my trailer for delivery today an engine for a car dealer in Peterborough. I'm sure some guy with a broken down car is anxiously awaiting his replacement engine so the mechanics can get started installing it.
My company picked it up yesterday and it'll be delivered by noon.
Put it it on a train? Still has to get to the rail depot by truck, still 3-5 days to get to Toronto (rail yards are only in major cities), and then it has to be unloaded, put on a truck, backtracked all the way east back out of the city and up to Peterborough. In the end it could very well take over a week.
If if you're that guy waiting for his engine, does this sound reasonable?
Rail serves a good purpose when it comes to non time sensitive long haul. Time sensitive long haul or regional or inter-provincial medium haul is dominated by truck as its vastly more effective. And your local mom and pop shop, grocery store, beer store, hardware store (etc etc ad infinitum) is never going to get deliveries via train.
As for pollution, you'd all be amazed at how clean the new trucks run. Read up on the science of DPF and SCR. Comparing to trains which are still allowed to burn high sulphur furnace oil with NO aftertreatment of the exhaust shows a lack of understanding again - locomotives are very VERY dirty in comparison now.