This study examines word order variation in wh-interrogatives with adjuncts (questions formed with “when”, “where”, and “how”) among bilingual Spanish-Brazilian Portuguese speakers and monolingual Spanish speakers in Misiones, Argentina. It investigates whether bilinguals differentiate word order in each language and whether geographical location (inland vs. frontier cities) influences this variation. Two tasks were used: an acceptability judgment task and a production task. Results revealed no significant differences between bilinguals in frontier and inland cities. However, bilinguals and monolinguals differed significantly: monolinguals were more sensitive to word order variation, rejecting SV and VS orders more frequently and showing higher acceptance of the canonical VS order in Spanish in comparison to bilinguals. Bilinguals, in contrast, demonstrated a preference for SV order in both Spanish and Portuguese, reflecting potential cross-linguistic influence. In production, monolinguals favored the SV order when presented with VS stimuli, while bilinguals maintained greater flexibility in Spanish word order. These findings highlight the influence of Portuguese’s SV order on bilingual speakers and the distinct syntactic behavior of monolinguals, contributing to research on language contact and bilingualism in closely related languages.