While it may be simple it would be contrary to the supreme law of the land - the Charter - as set out by the SCOC in the 1985 Singh decision.

Every person physically "in Canada" has the right to "fundamental justice" (our version of due process) that has come to mean an oral hearing before the Refugee Protection Division on the merits of the claim to Convention Refugee status.

The federal government engaged in a sleight of hand to get around some aspects of the Singh decision. In a technical legal sense a person at a Port of Entry (border crossing) is not considered "in Canada" so Safe Third Agreement designating the US allows claimants seeking entry at a POE to be referred back.  That does not work when the person enters Canada by crossing the border at a place other than a POE.

Also note s. 133 of the IRPA that says such entry is not to be penalized as illegal for refugees which implements one our international obligations under the UN Convention on Refugees.