The visa waiver program allows natives of 36 countries – Ireland, Britain and many other European nations among them – to enter the U.S. without a visa for business or pleasure stays of up to 90 days.
Those traveling under the program should know that they cannot extend their stay in the U.S. beyond 90 days . . . unless a documented, serious emergency arises, in which case the traveler can apply for “satisfactory departure” which would, if approved, allow for a further 30 day stay in the U.S.
Satisfactory departure is definitely not granted as a matter of routine, and the emergency that arises must be either medical in nature, or something that prevents travel out of the U.S. at the required time from taking place. (For instance, the volcanic ash that prevented trans-Atlantic flights earlier this year would have allowed for satisfactory departure to be granted.)
You say that your relative would like to stay for extra time to investigate business opportunities. Satisfactory departure would definitely not be approved for such a reason.
Ordinarily, satisfactory departure must be applied for through the U.S. Citizenship and Immigration Service. Evidence of the emergency – for instance, a note from a doctor or hospital – would have to be presented, and a USCIS officer would decide whether or not to approve the request.
Those who were stuck at the airport for days on end during the volcanic ash cloud wouldn’t have had to go to a USCIS office to apply for satisfactory departure, nor would travelers who are detained at an airport due to unforeseen events, such as weather/mechanical delays. They should keep evidence of the problem that caused the delay to avoid problems if and when they wish to return on a visa wavier to the U.S.
You ask if your relative can travel to Canada for a short while, and then return to the U.S. for another 90 days. The answer is no.
According to the point of law, “An alien admitted to the United States under (a waiver) may be readmitted to the United States after a departure to foreign contiguous territory or adjacent island for the balance of his or her original visa waiver pilot program admission period if he or she is otherwise admissible and meets all the conditions of this part with the exception of arrival on a signatory carrier.”
In other words, if your relative travels to Canada on day 50 of his 90 day authorized stay, and returns on day 52, he will be readmitted to the U.S., but only for an addition 38 days.
There is nothing stopping your relative from returning to the country from where he came and subsequently coming back here, as there is no point of law that says a visa waiver traveler must remain outside the U.S. for “x” number of days before attempting to return again.
However, frequent 90-day trips to the U.S. using the visa waiver would certainly arouse suspicion that the traveler has established a base here. If a traveler cannot prove the intention to return to a permanent base abroad after the 90 days are up, permission to enter the U.S. can be denied.