Line a 9-by-9-inch baking pan with parchment paper, and gently brush it with canola oil.

In the bowl of an electric mixer fitted with the whisk attachment, sprinkle the gelatin over 1/2 cup cold water; let stand for 10 minutes to allow the gelatin to bloom.

In a medium saucepan, combine sugar, corn syrup, and 1/4 cup water. Place saucepan over medium-high heat and bring to a boil. Boil rapidly for 1 minute, then remove from the heat.

With the mixer on high, slowly pour the boiling syrup down the inside of the mixing bowl into the gelatin mixture. Add the salt and vanilla and continue mixing for 10 to 12 minutes.

Brush oil onto a rubber spatula. Pour the fluffy marshmallow mixture evenly into the prepared lined pan. Cover with more parchment paper that has been brushed with oil. Let sit at room temperature for 2 hours.

Remove the marshmallows carefully from the pan. Place marshmallows on a cutting board covered with powdered sugar. Brush knife with oil to prepare for cutting the marshmallows. Cut marshmallows into 1-2-inch squares (depending on the size you desire). Place marshmallow squares one at a time into a bowl with powdered sugar. Toss each marshmallow with powdered sugar until well coated. Marshmallows will keep for a few weeks in an airtight container.