Burger King Worldwide Inc. executives defended their planned acquisition of Tim Hortons Inc., saying that global expansion ambitions rather than tax considerations are behind its deal for the Canadian-coffee-and-doughnut chain.

Miami-based Burger King confirmed on Tuesday plans to buy Tim Hortons for about $11 billion, creating a new fast-food giant that will be based in Canada. The relocation of such a high-profile American brand drew new scrutiny to the debate over so-called tax inversions at a time when U.S. lawmakers...