Government grants and contracts, where the government is involved. Otherwise it's engineers, doctors, pre-docs and post-docs, and private corporations.
The American university has been like a civ building for a few generations. You plunk one down and immediately get +2 research. But then it's started to move to +1 research / +1 gold. And we have to be a little bit concerned that it's going to become +2 gold if the trend continues.
We're still a pretty solid research leader. The 3d Printer came out of Raleigh, North Carolina. I mean who would have thunk it, right? You'd expect that to have come out of MIT or Silicon Valley. But nope, it didn't. Buuut, the world is changing. Technology has improved. Universities don't have a stranglehold on the means of production anymore and that is not entirely a bad thing. I do not fully understand the problems but I do know they're complex. A dilution into the social sciences probably doesn't help, but neither does the prevailing academic policy of "publishing quotas". Feynman once said that when Einstein stopped teaching it was the end of his productive career. A lot of research goes on under the auspices of DoD contracts as well.
The Canadians, or frankly anyone not us, will always be anxious to poach productive researchers. Brain drain should always be a concern. It's more an indication that the rest of the world is becoming more stable, more affluent, and free than it is an indication that we are becoming less so.