Previous studies have observed different gender assignment strategies for English nouns in Spanish-English code-switching (CS). However, these studies have not investigated the role of noun gender canonicity of the Spanish equivalent, they have only examined participants in bilingual speaker mode, and most studies have not explored the role of bilingual language experience. The current study compares gender assignment by heritage speakers of Spanish in a monolingual speaker mode and a bilingual speaker mode, considering the role of noun gender canonicity and CS experience. Results revealed a language mode effect, where participants used significantly more masculine determiners with the same feminine nouns in the CS session than those in the Spanish monolingual session where they used a feminine determiner. Further evidence of a language mode effect was found in the effect of noun canonicity and bilingual language experience. Noun canonicity was only significant in the Spanish monolingual session, where participants used significantly more masculine determiners with non-canonical nouns. Bilingual language experience was only significant in the CS session, where regular code switchers used more masculine default determiners than infrequent code switchers and non-code switchers, while in Spanish-only, all these groups behaved similarly