The cite you provided looks like an official Canadian government website. But, it's not.The
“ may” part is after paying 1,000’s of dollars
So on face value
A felony conviction prohibits anyone from entering Canada
It is run by a law firm that is eager to help people apply for a "Temporary Resident Permit".
They include this page, which outlines how to rehabilitate your record. Yeah, it will incur costs.
But, you are way off base in making such blanket, absolute statements. You write as if any American with a felony conviction, no matter how old, cannot get into Canada. That is not true.