These sentences are similar, but slightly different. "WOULD" is used as a condition of something in the past tense. "If I HAD a lot of money, I WOULD buy a house." "What WOULD you do if you TRAVELLED to Canada?" ---- "WILL" is used as a condition of something in the present tense. "If I HAVE a lot of money, I WILL buy a house." "What WILL you do if you TRAVEL to Canada?" Hope that helps!

I agree with what everyone is saying here. That the sentence containing "would" is asking the listener what they believe the speaker would do if certain conditions were met or if something in particular happened, and that the sentence containing "will" is asking the listener what they believe the speaker will actually/definitely do. Examples: -- Would -- 1. What do you think I would do (if I won a million dollars)? 2. What do you think I would do (if I locked myself out of my car)? 3. What do you think I would do (if I were offered a job in Japan)? -- Will -- 1. What do you think I will do (tomorrow when he starts screaming at the girl for no reason again)? 2. What do you think I will do (later tonight when he doesn't put his phone down while we are eating dinner)? 3. What do you think I will do (after I pick him up at the library tomorrow)?

Either can be used as they are almost the same. "What do you think I would do?" means to speculate or conjecture - what might I do? It's a possibility. What do you think I will do? generally means that I am going to do it. It's definite.

1: hypothetical. 2: predictable.