Can I choose what products to upsell on the product page?

I want to choose specific products to appear on the upsell widget. Is this possible?

No, not at the moment. The products that appear in the recommendations are based on your store's previous orders history and there is no setting in the app yet that allows you to choose your upsell products. If you want to personally choose your products to upsell, you can check out Discounted Cross Sells, another great app from Booster Apps!