The Globe and Mail reports in its Tuesday edition that when the loonie falls Canadian investors traditionally start to buy domestic exporting stocks. The Globe's Scott Barlow writes that the rise of Mexico as an exporting powerhouse means this time, an export-heavy investment strategy may disappoint. There are 34 members of the S&P/TSX composite index with more than 35 per cent of revenues generated in the United States. For some, like forestry stocks Interfor and West Fraser Timber, there is little competition from Mexico and a weaker loonier will help boost earnings. Financially based companies like Brookfield Asset Management and Manulife Financial have little to worry about from Mexican rivals. The outlook is much less clear for domestic companies with both direct and peripheral links to manufacturing and exports. Companies such as Magna International and ATS Automation Tooling Systems may not reap the same rewards from the weaker Canadian dollar as in times past. A weaker loonie is good news for Canadian exporters, but investors will have to be more careful with stock selection. Making sure a firm does not compete with Mexican manufacturers is now job No. 1.