Almost everything is okay - it is just that sometimes you need to get the right paperwork.
You need to fit into the right category in order to be able to do what you want in what is actually a foreign country.
And there are a lot of available categories.
The examples I referred to in my post are just there to illustrate the hoops that your country puts some people through.
True (if somewhat dated) story:
I worked as a Canadian customs and immigration officer during two years in the 1980s. I dealt with an individual who was publishing a local newsletter targeted at people in small communities on either side of the border. For a while he was handling everything including advertising sales on both sides of the boundary. He was a US citizen and resident.
He arrived at the border as usual one day on his way to see some potential Canadian advertisers. He was referred for secondary immigration examination. It was determined that he had been working (selling ads) in Canada for some time, without a work permit.
When I last heard, he was detained and being considered for permanent deportation - which would mean being barred from ever entering Canada again.
The only difference if the situation had been reversed and he had been a Canadian selling ads in the US? The deportation would have been more likely, and the border and immigration authorities would have been much more heavily armed (the cells in the US were also much more extensive and heavily used).
There are a whole bunch of new rules since then which make it much easier to either obtain a permit or fit within an exception that doesn't even require a permit, but you need to educate yourself about the restrictions and requirements concerning what you intend to do. I certainly am not the person to ask about the details.