if you want to ensure that you don't get stopped at the border, do the following:

1) be sober.
2) dress like a respectable adult.
3) be honest.

it's your choice of clothing, in conjunction with your skin colour, that is going to get you stopped, not your history of drug use.

if you must show up with chains around your neck, prominent tattoos and messy facial hair, they'll be more likely to let you through if you admit it. the thing that's most likely to get you stopped is if they think you're lying to them - and they will think you're lying to them, even if you're not.

the only problems i've had at the border are with people noticing that i'm tanned, and then questioning me on my status as a canadian. i don't know if they thought i was mexican or something else, but the only reason they've ever stopped me is on that suspicion of lying to them about my citizenship - and this is with advanced clearance.