Ok, I've been down this road. I was turned away this summer for DWI, and researched this in depth.
First, bring your passport. When going through the boarder crossing have everyone's Passports, Licence, and your registration and insurance proof all collected. They will ask you some questions trying to suss you out. They told me it was rude to talk to them with sunglasses and made me take mine off. This year I thought my passport was in my glove box and it wasn't so I got searched. When they ran my records they found my DWI and turned me around. As you need a passport (only started in July of this year), I just went climbing in Index and explored the cascades this summer.
I've been to BC twice before and used to live 1 hour from the boarder in upstate in NY. In Quebec they don't give a fuck, and I have never had trouble crossing there. That I-5 boarder crossing, above Seattle is the worst. I crossed there in 2002 to go to Squamish. They searched my car and found a roach in the ash tray. Threw us in a white room and grilled us for the location of suspected Cocaine. Of course there was none. After about an hour they let us go. The next customs people asked if we had any money on us. I responded with how much cash I had and they said I didn't have enough money to enter the country, though we had bank cards. In the end we made it though with a 5 day pass.
The next time I crossed in SweetGrass, which is in Northern Montana, to go to Banff. This time they sqabbed our dash board and said they knew we smoked weed in the vehicle within 48 hours. I explained we had, but stashed all our weed in the US because of my previous experience. They didn't care at all about my dog, and after I leveled with him, describing my previous experience, he ended up being super cool and let us pass.
Bottom line. Try to look legit, have all your papers, and don't be high and they will probably just waive you through. If you do get searched, don't lie, because if you got your DUI outside of 5 years they will let you in. This involves being REHABILITATED, and is really BS and totally at the boarder cops discretion. Sometimes it entails a fee, sometimes not. Just try to be as cool with them as possible because they have the power and also have access your criminal records.