Medicinal plants are an important component in Indigenous cultures. Aralia nudicaulis L., Rubus idaeus L., and Rosa arkansana Porter were analyzed for total phenolic compounds, carotenoids and antioxidant activity by DPPH (2,2-diphenyl-1-picrylhydrazyl), FRAP (ferric-reducing antioxidant power), and ABTS (2,2-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid). The samples were harvested in Saskatchewan, Canada, with the help of an Indigenous Traditional Knowledge Keeper and the analyses were performed by spectrophotometry. The results showed that total phenolic compounds amount ranged from 0.08 to 0.88 mg GAE/mg d.w. and the total carotenoid contents ranged from 0.03 to 1.26 mg/g d.w. The in vitro antioxidant activity ranged from 0.02 to 0.71 µmol TE/mg d.w. by DPPH, from 0.05 to 2.53 µmol TE/mg d.w. by FRAP, and from 0.04 to 1.06 µmol TE/mg d.w. by ABTS. Rosa arkansana leaves stood out with higher amounts of total phenolic compounds (TPC) (0.88 ± 0.02 mg GAE/g d.w.), carotenoids (TC) (1.26 ± 0.03 mg/g d.w.) and antioxidant activity (TAA) by DPPH (0.71 ± 0.01 µmol TE/mg d.w.), ABTS (1.06 ± 0.01 µmol TE/mg d.w.) and FRAP (2.32 ± 0.01 µmol TE/mg d.w.), with the same amount of Rubus idaeus belowground (2.53 ± 0.01 µmol TE/mg d.w.) in last technique (2.32 ± 0.01 µmol TE/mg d.w.). The first principal component describes 83.88% of the total variance and all the variables have high influence on this component (factor loadings: T = 0.976, TC = 0.735, TAA by DPPH = 0.955, FRAP = 0.894 and ABTS = 0.996), demonstrating that these samples do not have large dissimilarity. The second principal component represents 13.