I very much doubt it. My information isn't very uptodate, however I have heard plenty of stories of westerners being allowed to cross the border easily ... But then have great trouble getting back out (until they've paid off the border guards that is).
Additionally, if you cross from Chiang Rai, I don't think the Burmese let you travel very far into the country.
This could have all changed again by now as the country is indeed opening up. Slowly. almost 5 years ago