I have traveled to Asia and Europe for work, but never had more hassles than trying to get into Canada. The first time was for an install. I got off the plane in Edmonton and got directed over to customs. They said I needed something stating that my work was part of the original purchase, and not a separate order. My customer faxed Customs a letter stating that was why I was there. The Customs lady showed the fax to a co-worker and started laughing. Not until my customer produced an order that stated that start-up service was provided with the original purchase price was I allowed in.
Incident #2 was driving across the Peace Bridge. I had 8 modules with me that I was going to swap out(under warranty) on drives installed in Canada. I was going to bring back 8 modules. I got sent to the Customs office where I was encouraged to get a broker. I would have to pay the tariff, then apply for a refund when I brought back the other 8 units. The Customs lady set me up at a PC, gave me some very brief instructions, then went back to reading her book. I completed it, but still not sure I did it right. I paid the tariff and went on through.
Incident #3 was again at Peace Bridge. I had a PO from end customer in Canada to the equipment OEM(my customer) and a PO from the OEM to me for a service call. That wasn't enough to get in, since a Canadian citizen should have first dibs on doing the work. I went back home and my customer had fill out a lengthy application stating that only I was capable of doing the work. They stated the a college degree was needed for this type of work. When I went back a week later, I almost didn't get in, since the application stated a college degree was needed, and I didn't bring mine with me to show I had one. The lady had mercy on me since I was already turned away once. By the way, since Canada turned me away the first time, I was flagged by the US as a problem. I got pulled aside trying to get back to the US and had to wait in the building for quite a while before before being interviewed and allowed back into the US.
If you take tools with you, you are going to get hassled. If you normally carry a toolbox in your car and are just going across for a meeting, you better empty your car of any tools. I have also been advised that to just say you are going in for a meeting and only take your laptop. Use tools at your customer site if possible. My counterparts in Canada tell similar stories of trying to get into the US.