On PokerStars the cards are not predetermined. You have an Entropy generator created by Intel that uses random numbers in conjunction with user input (player mouse movements, player response time, etc.) to generate what will happen.
So if you shove the flop and win. Then suddenly you go back in time and make the same move, but this time it takes a split second longer for them to receive the data, and/or you move the mouse slightly differently, you are probably going to see different turn and river cards.
As for people seeing patterns, that's a human problem. We're designed to look for patterns, so we see short term anomalies (which aren't really anomalies) and give more credence to them than we should.
For example, the computer will see the cards as:
Card #1, Card #34, Card #50, Card #17, Card #11 (really they're ones and zeros, like 0010, 1001, 0110, 0111, etc.). But we look at it and say "Hey, those are all spades!" or "Hey, they came up 2/4/6/8/T!" or whatever. The computer doesn't care about or understand concepts like flushes or straights or that. It's just data. It doesn't even look like a pattern if you could see what the computer sees. We create the patterns in our heads.
In the IT business, we say "The problem is between the chair and the keyboard."
.
