I have not read the book yet. So I am only basing this question off the movie. My thoughts are Total Recall was true. He never fully got his implant. Recall triggered his memory in the past.
Let's start with the obvious, You are not suggesting that Total Recall was a true story. With that out of the way, some of the acting in the movie was definitely a little on the fake side but I reckon the actual story was memory not implant. Having said that, I have read this book and don't worry I've not given away any spoilers.
If you read the P k d original short , you'll know the answer, We will remember it for you. (Wholesale) being a collection of stories, that contain this short.
What's your thoughts ?