Typically, weeds do not grow up through the pavers, but rather in dirt that gets deposited between the blocks when the polymeric sand has gotten washed/blown away....which happens over time. It is not impossible for them to grow up through, but if the excavation and subsequent base material compacting is done right, it's tough for them to do so. Roundup is readily available, and very effective, but can (and will) leach out and kill grass on the sides of the paver walk/patio...so be judicious when using it.
Roundup makes a product that says it will keep them out for several months.....but weeds to not watch TV or pay attention to their claims, and have a way of reappearing.