Ship long enough and you'll likely encounter a delay because of an issue with a Customs agency. Sometimes the delays are due to random inspections by an agency but quite often delays are a result of insufficient information or errors in the documents presented for customs.
It's important to note proper completion of all necessary documentation is the sole responsibility of the shipper. If you are a shipper exporting goods to another country, then you are responsible. If you are importing goods into Canada from another country, the shipper in that country must provide accurate and complete documentation to you.
Ultimately it is incumbent upon you as an importer and/or exporter to learn about rules, regulations and the necessary documentation required by the countries with which you conduct trade.