First: It's always best to properly season (dry) your cooking wood. As it will produce a cleaner fire and better tasting food.
The more sap - the more possible soot.
The only wood that I've used green to cook with is "apple" (see exception below
) and it worked real well. The thing you must watch out for when using green wood is soot. With most woods, soot will leave a dark, nasty tasting layer of build-up on your food and inside your smoker/grill.
The very first time I used a smoker, I used "green" mesquite. There was smoke billowing so dense from my little "bullet" smoker that cars passing by my house literally disappeared into the cloud. I was smoking two hams at the time and they came out pretty black.
The bark had a sort of numbing effect on the tongue. But, the inside meat was pretty good.
Maple is a pretty light flavored wood so you may be able to use it in limited amounts. I would start by doing a "test" cook with a small amount of food to see how it tastes. Also check to see if you're getting soot on the food and inside the cooking chamber.
Hope that helps.