So, i got one of this cheap 3$ L298N drivers they sell in ebay. Max current for it is 2A per channel or 4A max. Can I use the 2 channels to drive a single motor of like, 2.5A? If yes, how would i do that?
Which motor exactly? Do you have a data sheet? Those cheap driver boards rarely put out their rated power and a large heatsink is required to get anywhere close to the max rating. You'll probably be lucky to get one amp out it.Good news is that it's cheap so if you do cook the chip you're only out a few dollars. 
so its worth a shot if you already bought it.
It´s a linear actuator, i used a bench power supply to measure it´s current and it stays lower than 2A most of the time, sometimes it can go above 2A. If i just connect the 2 channels M+ (A and B) to one of the motor cables and the other 2 M- (A and B) to the other cable, will it work?
https://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf yes but follow the datasheet. page 7
Did it occur to you to look at the datasheet , (page-7) ?