11 times teams have beaten St. Louis Blues en route to a Cup:
68 MTL
69 MTL
70 BOS
72 BOS
77 MTL
97 DET
98 DET
99 DAL
01 COL
02 DET
12 LA
31 times teams have beaten Boston Bruins en route to a Cup:
27, 28, 30, 31, 40, 43, 45, 46, 48, 49, 51, 53, 57, 58
68 MTL
69 MTL
71 MTL
74 PHI
77 MTL
78 MTL
79 MTL
80 NYI
83 NYI
86 MTL
88 EDM
90 EDM
91 PIT
92 PIT
95 NJD
03 NJD
13 CHI
I notice that since expansion, the only teams that beat the Bruins en route to the Cup were teams that would win multiple Cups. The 68-69-71 Canadiens. The Flyers won two Cups. The Canadiens again. Then the Islander dynasty. Montreal with Roy went through them. Then Edmonton's dynasty. Then Pittsburgh. Then Scott Stevens' Devils. Then recent Chicago.
Further, each of the teams except Dallas who beat the Blues won multiple Cups, which is fitting since 99 SCF G6 remains suspended in triple OT forever. Tainted Cup, kind of doesn't count for the category.
If Boston wins Wednesday they automatically fit this category whereas it means if the Blues win they will go on to win multiple Cups!