He will remain in Washington to "oversee the American response to Syria", the White House said.
Vice-President Mike Pence will travel in his place to Peru for the Summit of the Americas and then Colombia.
Medical sources say dozens were killed in the alleged attack in Douma, but exact numbers are impossible to verify.
Syria and its military backer Russia have denied any involvement in Saturday's incident. They have invited inspectors from the Organisation for the Prohibition of Chemical Weapons to visit Douma.
Will there be a military strike?
Mr Trump has pledged a "forceful" response, and has spoken of numerous military options.
Last April, after a Sarin nerve agent attack killed more than 80 people in a Syrian opposition held town, Mr Trump ordered the firing of dozens of cruise missiles at a Syrian government air base from US Navy ships in the Mediterranean.
It was the first direct US military action against forces commanded by Syrian President Bashar al-Assad.
Since Saturday's incident, Washington has been in discussion with Britain and France, raising the prospect of co-ordinated Western military action.
The AFP news agency quoted French government spokesman Benjamin Griveaux as saying on Tuesday that "if a red line had been crossed, there will be a response", adding that intelligence shared by the two leaders "in theory confirms the use of chemical weapons".
Russia has warned at the UN Security Council that US military action could have "grave repercussions".
What happened on Saturday?
Syrian opposition activists, rescue workers and medics allege that bombs filled with toxic chemicals were dropped on Douma, in the Eastern Ghouta region, near the capital Damascus, by Syrian government forces.
The Syrian-American Medical Society said more than 500 people were brought to medical centres with symptoms "indicative of exposure to a chemical agent".
It said this included breathing difficulties, bluish skin, mouth foaming, corneal burns and "the emission of chlorine-like odour".
Neither the death toll nor what exactly occurred can be verified as the area is blocked off with access denied.The estimates of how many people died in the suspected chemical attack range from 42 to more than 60 people, but medical groups say numbers could rise as rescue workers gain access to basements where hundreds of families had sought refuge from bombing.
The French representative at the UN Security Council said poison gas had deliberately been used as it could seep down to the basements.
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