Tell them you go shopping in Ontario 2 - 3 times per year because of the favourable exchange rate. Have an idea of where you could say you go shopping - Yorkdale Mall, Vaughan Mills Centre, Milton Premium Outlet Mall. Tell them you buy clothes for work - suits, shoes, ties or something similar that matches your actual occupation. Keep your answers short and matter of fact. When they ask you questions, use the word 'I' or me often, and make it personal, such as:
I like going to the stores in Canada because the exchange rate allows me to save alot of money.
I get better selection at the stores in Canada
It's worth it for me to drive across the border and get the items I want. I have had good success shopping at stores in Ontario.
It is not far for me to drive to Ontario for shopping. I only live 2 hours from the border.
The border guards try to create a narrative that you are doing something that is unusual and not in your best interest. As in, we should be suspicious of you because what you are doing what a normal person would do. You correct them through matter of fact statements that do make sense.
When I cross the border, I get sent to secondary screening all the time. They go through my car, my wallet etc. If you are a male, between 18 - 45, they will harass you. They have to harass someone to justify their existence as border guards, so single men are the most acceptable target versus women or the elderly. Another privelage of being a male, I suppose. That is the society we live in on both sides of the border.
I once went across with my wife, and then 30 days later, I went across with my girlfriend. They had record of both crossings but didn't ask me anything, nor did they care. When I go by myself, they always harass me. But, I just give matter of fact answers that are logical and easily explainable. And they eventually let me go on my way.
If you still have trouble, I will give you my personal contact info and you can tell them we are friends and that you are going to visit me and my family. If they call me or inquire, I will confirm for them.