Assuming that the European-based leagues are shutting down over the 2018 Olympics, then leagues like the KHL, SHL, and the Swiss League will supply players. For Canada and the USA, it gets a bit hazy. Players under contract with NHL clubs would have to be released (similar to how the U-20 World Junior tournament works). So you could see some AHL players (ones not with an NHL contract), and players from the low minors, the CHL and US college hockey.
The challenge is that the NHL does want to go to China in 2022 (Toronto has already made inroads in China by getting one of their networks to show their games; it's a huge untapped market that the NHL wants to get exposure to), so it's going to be a balancing act in that they can't completely burn the IOC. The problem is that the NHL wants the IOC to pay for transportation costs (which they've done in previous Olympics) and the IOC isn't having it. IMO this is an Olympic tournament put on by the IOC under their rules. As an example, if I travel for work to visit and do work for a client (sole purpose is to visit them), typically the client gets billed for my travel expenses (I pay and get reimbursed by my company who then bills back the client) which would include airfare (in Sochi the IOC paid for chartered flights for the NHL players), lodging, ground transport, and meals.