Cartels have boats, but no one's shipping drugs up to Canada just to smuggle them south: They just get shipped directly to the US
Trump is just making up an excuse to justify cutting off trade with Canada.
Really, the whole fentanyl thing seems like scaremongering: People do overdose on it, but you won't die from touching it or inhaling trace quantity. It's not even the most potent opioid known, not even close to it.
TLDR:
They found debugging commands that can be used to access the memory of the device over USB. This is as much a backdoor as any device that runs unsigned firmware
Unless you store secret files on your Bluetooth dongle, you shouldn't have to worry about this.