Conservation staff at Banff National Park in the western province of Alberta say they hope the three calves will be joined by seven more in coming weeks.
A herd of 16 plains bison, including 10 pregnant females, were successfully reintroduced to the park in February.
There used to be some 30 million bison in Canada until they were hunted almost to extinction in the 1800s.
About a quarter of a million remain on a sliver of government-controlled land and on private farms where they are bred for meat.
Banff's resource conservation manager Bill Hunt told the BBC the females are "doing a great job" and nursing well.
"The bison moms know what they're doing," he said. "Our staff are in the woods carefully hiding from the sidelines to see if everything's going well."
The first calf was born 22 April - Earth Day - which Mr Hunt said was "a bit of luck", rather than something planned.
All the bison cows are young and will be raising their first calves in the "soft-release" paddock, where they are being kept for their first 16 months in the national park.
Those first births, along with the park's natural barriers and wildlife fencing, will stop the bison from wandering astray when they are fully released into the wilderness, said Mr Hunt.
"When a female has her first baby, that ties her to that landscape," he said. "So it's one of the tools we use to try to keep them within the park area."
The bison will be kept under observation in that soft-release enclosed pasture of the park in the foothills of the Rockies until the summer of 2018.
Parks Canada first proposed bringing bison back to Banff in 2012, with the support of local indigenous groups.
"The day we brought the bison in was obviously a big deal," Mr Hunt said.
"But the symbol of hope that comes with the birth of these calves was really moving."
The first bison calves to be born in 140 years in Canada's oldest national park are taking their first steps.