In a small bowl, mix the sugar, brown sugar and cinnamon well.
In a separate bowl, whisk the egg whites and vanilla together until frothy, approximately 1-2 minutes.
Coat the inside of the slow cooker with cooking spray.
Place the pecans in the slow cooker and pour the egg white and vanilla mixture over the pecans. Stir to ensure an even coating.
Add the cinnamon and sugar mixture, stirring the pecans for an even coating.
Cover the slow cooker and cook on low heat for 2 to 3 hours.
Stir the pecans ever 20-30 minutes. If necessary, add a little water towards the end of the cooking time (last hour).
Remove the pecans from the slow cooker and place on a baking tray or parchment paper to dry, cool and ensure a crispy coating.
Store in an air-tight container.
Notes
After making the recipe, feel free to adjust portions of sugar and cinnamon. Not sweet enough? Add more sugar. Too sweet? Add a teaspoon of salt to the dry mixture.