The accident happened late Sunday night when the truck hit the 81-unit eastbound freight next to a highway a few kilometres east of Oxbow. The train was heading for the northeastern United States.
The 20-year-old truck driver from Manor, Sask., was treated for minor injuries and kept in hospital overnight for observation.
The RCMP said six of 22 cars forced from the track by the impact leaked their cargo of light crude oil.
But CP spokesman Kevin Hrysak said rail crews determined only one car leaked oil.
"It was a minimal amount and it was immediately contained by first responders, who set up a berm around the car, so there is no further product leaking to the surrounding property."
He said no private land was affected as the spill was contained to CP's right of way along the track. There are no waterways in the area.
The highway was temporarily shut down, as was the track. But Hrysak said the derailment wouldn't affect train traffic.
"This track actually isn't even a secondary line for us," he said. "It's more of a third line, so it's not our mainline traffic and there is no impact to other...customer traffic as a result. Everything can be detoured around."
He expected the track would reopen sometime Tuesday afternoon.
RCMP Sgt. Chris Boardman said investigators working to determine what happened were told the truck didn't appear to be speeding.
"The engineers who were operating the train...didn't think that it was going overly fast when it was heading towards the train," he said.
The derailment was the second in as many days. On Saturday, more than a dozen grain cars on a Canadian National Railways freight train plunged off a trestle near Wainwright, Alta. The bridge was damaged but no one was injured.
There were two other derailments in Alberta last week.