2020 The Authors. Food and Energy Security published by John Wiley & Sons Ltd on behalf of Association of Applied Biologists Drought stress due to water deficiency threatens production of canola worldwide. Carbon isotope discrimination (Δ13C), a trait that can be used to assess efficient water use, provides an opportunity to exploit natural variation in canola for stable production. Here, we show that substantial genetically controlled phenotypic variation in water use efficiency (WUE) component trait, Δ13C (20.4 to 23.6‰) exists among accessions of canola. Quantitative trait loci (QTL) analysis revealed ten loci for Δ13C, each accounting for 2.5% to 16.5% of the genotypic variation. One of the significant QTL for Δ13C was co-localized with a QTL for flowering time, a trait implicated in drought escape and was mapped in the vicinity of the FLOWERING LOCUS T (FT) on chromosome A07. Gene expression analyses revealed that among FT paralogs, BnC6.FTb expression was significantly correlated (r = 0.33, p <.01) with variation in Δ13C across at least two environments in a canola DH population. Integration of data based on instantaneous single leaf gas exchange, dry matter Δ13C, and whole plant measurements suggests a possible trade-off between early flowering and WUE. Our findings provide insights into the complexity of Δ13C and WUE which could enable the development of canola varieties resilient to drought and increasing canola productivity under water-limited conditions.