The M4 is similar to the C7 used by the Canadian army - both are derived from the AR15 platform. 

Like a C7, I would expect the M4 to be a restricted firearm.  If the fellow has all the correct licensing and paperwork, he ,may be able to import it.   I’m not current on the prohibited list, but I’m sure it can be looked-up online someplace.

If it is a M4A, then you are likely out of luck.

> On 29-May-2017, at 16:28, TJ Hemrick <x53gunner@gmail.com> wrote:
> 
> Hey guys,
>  I found a Vanagon north of the border I want to trade a guy my gun for
> (an M4 with all the goodies for those wondering) but he's unsure what the
> laws are regarding owning a long rifle up there.  Any of you know for sure?
> 
> Thanks,
> 
> TJ