Sounds strange, but the rules do say "Award travel is not permitted on select flights", so this may be one of those cases, as travel is permitted "within the continental USA" and apparently does not have to originate in Canada. (Page 38, Cdn+ program guide) Perhaps you were trying to combine CP and AA (i.e. how were you getting to New York?) on a single award, but this should not normally be a problem.
I know AA considers its non-stop New York to LAX and SFO flights as a special category of service, but I have not noticed such restrictions on the AA redemption charts.