This study investigated Ontario university STEM students’ past experiences with STEM cross-curricular elements in the Grade 12 mathematics courses Advanced Functions (MHF4U), Calculus and Vectors (MCV4U), and Data Management (MDM4U), and their perceptions of how the cross-curricular contents prepared them for their STEM studies at the university level. An online survey was distributed to Ontario STEM university students, and collected 364 responses, with 95 deemed suitable for analysis. Participants rated their experiences with STEM content in each Grade 12 course, as well as the perceived effectiveness of the courses in preparing them for STEM studies. Their qualitative responses provided additional insights into students' experiences with cross-curricular content. The findings revealed both strengths and areas for development in Ontario's Grade 12 university-level mathematics curriculum, particularly the need to align the contents with the demands of university-level STEM programs.