Hi Kei! So where I live, I had to apply for us to get a marriage license at a minimum of 3 days before the wedding. When my husband was crossing the border for the weekend for the ceremony, he did not mention that he was going to get married. But the officer was really pushing like "ARE YOU SURRREEEE youre not doing anything else this weekend...?" and he sheepishly finally said "Im also getting married". They pulled him inside just to explain to him that crossing in the future may be a little more difficult. Not because he didn't willingly tell them he was planning on getting married (although they did scold him a little), but because of the whole intent of return thing.
The border people feel like "big brother" lol. They are all knowingly. Don't lie to them. As long as you arent planning on coming over, getting married, and staying for like.. 3 weeks or months then I think they will be fine with you crossing with intent of marriage. My husband jsut said he was staying the weekend and that wasn't an issue. I'm thinking that they knew we were going to get married very soon because of the license I applied for us. I was shocked they knew though still. If you don't have to apply for a license, I still recommend just telling the truth... it's not illegal to get married as long as you intend to return, but you really don't wanna look fishy hiding things.