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* U.S. tariffs on $200 bln worth of Chinese goods expected in Sept
* U.S., Canada upbeat on trade talks with deadline on Friday
* Dollar Tree, Dollar General down on bleak forecasts
* Campbell Soup falls on plans to sell two units
* Futures down: Dow 0.24 pct, S&P 0.17 pct, Nasdaq 0.20 pct (Updates prices)
By Shreyashi Sanyal
Aug 30 (Reuters) - U.S. stock indexes were set to open lower on Thursday as optimism over U.S.-Canada trade talks was overshadowed by concerns over Washington's tariff dispute with China, which has been the bigger weight on the market for most of the year.
Washington has proposed slapping tariffs on a further $200 billion worth of Chinese goods after a public comment period ends on Wednesday, Sept. 5.
As the earnings season winds down, the Sino-U.S. tariffs dispute is again set to dominate investors' minds, despite the United States and Mexico striking a trade deal and growing optimism over U.S-Canada trade negotiations.
"I think this is an environment in which, if not for trade news, then we would be trading higher and we have seen that with the bumps in the Mexico trade talks," said Art Hogan, chief market strategist at B. Riley FBR in New York.
"We've had a pretty significant run and I think that we don't have any more good news to keep that momentum going which is why we're giving up gains, but very modestly."
The benchmark S&P 500 has hit a record high in every session since Friday, and gained 2 percent in the period. In comparison, the trade-sensitive S&P industrials sector has risen 1.61 percent, while the technology sector has increased 3.33 percent.
Shares of Caterpillar dropped 0.6 percent in trading before the bell and other industrial companies also dipped.
Among technology names, Apple was up 0.24 percent. Amazon.com, which is poised to join Apple in the $1 trillion market cap club, was slightly lower after having risen to top $2,000 earlier.
At 9:02 a.m. ET, Dow e-minis were down 64 points, or 0.24 percent. S&P 500 e-minis were down 5 points, or 0.17 percent and Nasdaq 100 e-minis were down 15.5 points, or 0.20 percent.
Shares of Campbell Soup dropped 1.2 percent after the company said it would sell two businesses that bring in about $2.1 billion in annual sales, about a quarter of its overall revenue.
Cloud software maker Salesforce.com fell 2.3 percent after its profit forecast for the current quarter fell below estimates.
Among retailers, Signet Jewelers jumped 14.7 percent after the company topped sales and profit estimates and raised its full-year sales forecast.
But, Dollar Tree slid 5.9 percent and Dollar General was down 2.7 percent after they gave disappointing full-year profit forecasts.
Commerce Department data showed consumer spending increased strongly in July and Labor Department data showed the labor market remained robust, despite a rise in jobless claims last week. (Reporting by Shreyashi Sanyal in Bengaluru; Editing by Shounak Dasgupta)