It's not Belvest anymore. In the past two years Prada has taken almost everything down a notch in order to save money (their sneakers, which were always made in Italy, are often made now in Vietnam and so forth), and this includes the suits. As well, the typical Prada customer doesn't care too much; they want a style and a fit and really don't care too much about canvassing. This, in addition to the cost-saving factor, probably lead to Prada's decision to switch. Why pay Belvest $1000 to make your suit when you can get the same amount of money from a customer and have to pay only $500 to another maker?
The newer models are mostly fused. That's not to say that they don't make some canvassed models at the top end, but nevertheless I believe their suit-production model has changed.
I've HEARD (note that this means I don't know for sure) that they switched to Lardini, who makes suits for many designers from Burberry to Dolce & Gabbana. This would make sense, since Lardini's suits are fused but nevertheless are amongst the top-end of fused suit makers.
Finally, Red, you're very welcome! I'm always glad to help out a fellow gaijin.