Even with a new tube, there may be portions of the original receiver reused. If any part has been recycled, the gun will automatically be a prohib.
If the mechanism cleared US ATF inspection, it will be a semi auto.
As far as importing one goes...
The manufacturer is going to have to be registered with US DOS for export of their products.
A licenced US exporter will have to handle the export.
The US DOS will have to issue an export permit; this will require submission of a Cdn. import permit. DOS may or may not allow export.
The firearm will have to be registered in Canada. This will require creation of a FRT number. All existing Suomi FRT numbers are for prohibited firearms. It is very likely the RCMP will want to inspect it, if you can get it out of the US.
It will be a restricted firearm, unless the barrel exceeds 18 1/2". As I mentionned above, it is unlikely that conversion to full auto would be an issue, if the firearm has been approved by ATF. ATF is rather thorough in determining if a firearm can be readily converted to full auto.