Not even close. A populist is a politician that latches onto whatever issue is the most prevalent in the public mind, then crafts his position to take the greatest advantage of it. He has no real principles of his own, and as such is comfortable changing positions on a dime if the public sentiment changes. He is equally as comfortable relying on conservative positions as he is liberal positions, because the positions are not based on core beliefs, but are a means to an end - gaining power. That is a good description of Trump.
Reagan was popular - people like who he was and had respect for his as a person - but his positions were based on conservative principles. He didn't change his positions just go along with the public mood, but sought to bring the public mood around to the principles he espoused.
Populism is a doctrine that appeals to the interests and conceptions of the general population. Reagan ran a national populist campaign against Carter in 1980. When Reagan started his campaign during the primaries, polls showed him trailing Carter by 40-50%. He gained popularity by his campaign and gained more popularity by following through after being elected. Trump is running a very similar campaign, now.
The biggest difference between Trump and Reagan is that Reagan was a previously elected public official. Trump on the other hand is not.
Trump built his entire company on Brand name. He is going to follow through with his words to the best of his ability, which is pretty damn good. If he didn’t, his family name and brand would be tarnished.
More over, most of Trump’s positions all fall back to a set of positions he has be trumpeting (no pun intended) since the ‘80s. Trade Deficits and Debt. Fixing these are part of his core principals. And to fix those, Trump has taken on positions that all connect back to those.
Trump isn’t it in it for power. He had an opportunity during the ‘80s and early ‘90s to run, but said that he liked what he did. He also said that he wouldn’t completely rule it out, especially if someone didn’t fix the Trade Deficits and Debt before we reached a point of no return. But he always gave hope that someone would. Obviously, that point has been reached as no one has done anything to fix it.