I completely agree with you that the probability of a tax on remittances to Canada would be quite low. However, there are other Trump related risks as well. e.g.747-captain said:Actually as deadbird pointed out, Trump did say (both on the campaign trail, as well as quite recently after assuming office) that he would tax remittances sent back home by undocumented immigrants.
However, one needs to understand that there are several nuances to this point. First off, there is no way on earth he could just "levy" a tax on everyone trying to send money out of the country (especially if that money was earned by someone that is lawfully present in the U.S.). Second, even if something like that were to be instituted, I'm not sure he could just unilaterally issue an Executive Order (like he tried to do with the Muslim travel ban). He would likely need to go through congress, and I would imagine that there are at least a few sensible Republicans who would not go along with an insane idea like that. Third, if something like this did ever come to fruition, there would be lawsuits flying around left and right, before this thing had the slightest chance of seeing the light of day! Trump learned that quite quickly that he is not King of the United States of America after that Muslim ban edict of his : Fourth, Trump has been all over the place with this issue. First he said that, then he said he would levy a 20% tax on all imports coming from Mexico to pay for the "wall" : (which was, of course, quickly shot down by members of his own party).
Also keep in mind that this "threat" by Trump was in regards to securing payment from Mexico : for constructing that infamous "Border Wall". So it was specifically directed towards Mexico and Mexicans. There is a ZERO chance of this happening to people sending money to Canada.
Another angle is hedging against currency fluctuations. Even if Trump isn't able to block remittances he might pass protectionist trade deals. These will likely cause turmoil in the currency markets. Having money on both sides in USD and CAD is a more defensive risk posture than keeping it in the US alone.