I would be happy to.
Cross-border surplus-stripping is unfortunately a bit of technical jargon. “Surplus” in this case refers to the retained earnings in a corporation. Normally when they are paid out, they are paid out as dividends. Dividends, when they cross a border, are generally subject to a 25% withholding tax, which can be reduced under tax treaties. In a parent-sub situation, it's usually reduced to 5%, but of course 5% is still more than 0%.
These cross-border—Canada to another country—surplus-stripping techniques, which is the extraction of these retained earnings from a Canadian entity up to its foreign parent, free of Canadian withholding tax, are of course contrary to tax policy. They typically rely upon an exemption under Canada's tax treaties whereby dividends might be subject to a 5% withholding tax rate, but a sale of shares of a Canadian entity can be tax-exempt under the terms of the treaty.
In very general terms, a dividend involves moving a certain amount of cash from Canada up to the parent, but when you sell shares, that also involves moving cash from the purchaser to the seller. If you contrived a situation that could be as simple as one Canadian subsidiary buying shares of its Canadian sister company from the parent, you can have money going from a Canadian company up to its foreign parent, but as proceeds from the disposition of another Canadian company's shares. That could be exempt from tax, absent these anti-surplus-stripping rules.