I will be really disappointed if it turns out he was one of the Fuentes clients as speculated.
It's 100% certain Cancellara doped during the 2000's: he excelled in an era when climbing rates were on order 5% higher than they are now, when day-to-day recovery was almost perfect. So if it wasn't Fuentes it was someone else.stage 17 of the 2008 Tour
"With the start of the climb over, O'Grady had done his work. Cancellara took over for CSC and the gap started to drop. He set a terrible pace, catching and dropping Di Gregorio and putting the sprinters off the back. Even white jersey contenders Nibali and Maxime Monfort (Cofidis) gave up the ghost. Jimmy Casper (Agritubel) had been dropped early in the stage and was now 18 minutes behind and nearly assured of being time cut."
Sure, it's not proof, but if it quacks like a duck, it's probably a duck. That was how people played with the big boys then.
When I think of guys during that era who may have stayed clear of the good stuff, I think of Thomas Voeckler. He finished 97th in GC. Did he train less? Was he inexperienced? I doubt it, and no, and he was younger then. But all of a sudden he becomes a podium contender simultaneously with VAMs dropping precipitously. I don't think Voeckler's VAMs went up, it's that others came back to him.