Heya Nefario, there are a whole lot of problems with US and Canada customs. You could have all the correct credentials, credit card, bank card, sponsors=US/Canadian citizen that sponsors you, if that agent you walk up to woke up on the wrong side of the bed, he'll deny you.
The computer systems, they run names, finger prints, iris recognition scans. You could come from a country that the US/Canadian computer systems cannot access, the guy could be a murderer/drug lord/arms dealer and get in to USA or Canada. Now for an example, I am a US citizen, I try to get in to Canada, they run my name through the computer system that they have access to US's computer systems, they ask if i have any criminal record, yea, I have a dui, they run my name find the dui, other records pop up from 1996, Paraphernalia and Grand theft auto, which I was never convicted of, but the records still show the reports. I get denied. But the murderer is able to get in because the US or Canadian computer systems don't have access to his country's computer systems because "they might be a poor country and or don't keep record". This is all as an example.
I am sure that US systems have access to British systems which Canadian is ruled under, as we all are allies.
This is so problematic it actually screws over a US citizen that wants into Canada or a Canadian that wants to get in to the US.
Since you are British, perhaps you can fly into Vancouver Canada and cross at a land based border crossing?
It would be worse, as it shows on his passport that he had tried to get in from china, and now he is in Canada trying to get in the US.
They will deny him without flinching.
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Sorry to hear about your loss trying to get here to the US. Best thing to do is go forward with a visa, get a sponsor if possible or a few references showing you have a few friends. If you do get in within the next year or more, do not stay any longer than the the time they give you. You might ask for 4 months, they might give you two weeks.
Since around 2007, they connected these computer systems all together to fight terrorism etc. Add to it, it screws over the tourists.
The entire situation with the borders/customs is screwed. Lookup youtube videos of denial of entry from and to the USA. You will find a lot of disturbing videos how cocky the customs agents are & we are neighbors.
Good luck to you in the future.