"Guarantee" is dependent on your supplement. For example, in Central it says (I'm paraphrasing) that insiders get first crack and helping and get to choose the route they want to work on by seniority order BUT total hours may not exceed 8 per day. Guess how enforceable this is when you're working 6 hours on the inside
? In practice, management lets drivers pick a person they want to work with and often plum routes (like malls) go to management favorites. AT BEST, you'll get to pick from what's left over -- best to find a driver you get along with and ask if you can work together.
Maximum hours may be covered in your supplement (mine's 8, like I said above) and enforcement is at management's discretion. Here, some years it's been 8, some it's been 12 and in others they haven't given a dang. 5 years ago they fired a pair of PTers for working over 12 (one got his job back, the other didn't pursue it) and then 2 years later I wound up working at least 80 hours per week...