Under whose jurisdiction does the bankruptcy law apply? What are the consequences for someone who has declared bankruptcy in Canada, is now living abroad, and cannot reach an agreement with their trustee regarding the excess amount owed? Will the bankruptcy be annulled and the person detained at customs if they return to Canada? Are they at risk of legal action abroad and/or wage garnishment? Can the excess amount owed to the trustee be contested?

Bankruptcy is a federal matter.

If you cannot reach an agreement with your trustee, you may not be discharged from bankruptcy. Your trustee will close your file, and all your debts will be reinstated as if you had not declared bankruptcy. Your creditors will be able to pursue you again.
You will remain an undischarged bankrupt, which is not grounds for arrest, but any assets you acquire will be subject to seizure by the trustee or your creditors.
Regarding surplus income, you can contact the Office of the Superintendent of Bankruptcy if you believe the trustee has miscalculated it.