Benjamin Albert Levasseur Onyshko
- Bats Right, Throws Left
- Height 6' 2", Weight 205 lbs.
- School Stetson University
- High School Vauxhall High School
Onyshko won three straight provincial championships in high school. Playing for the Canadian junior national team, he pitched 7 shutout innings against the DSL Mets and 3 against the DSL Phillies.  He was taken by the Milwaukee Brewers in the 16th round of the 2014 amateur draft, but did not sign. Going on to college, he was 1-1 with a 5.09 ERA as a freshman, 2-1, 4.26 as a sophomore. He had a 2-4, 4.83 record as a junior and 2-0, 2.60 as a senior with 46 K in 34 2/3 IP. The Seattle Mariners chose him in the 24th round of the 2018 amateur draft. The scout was Rob Mummau. 
He split his first pro summer between the Modesto Nuts (0 R in 2 IP), Everett AquaSox (1-0, Sv, 2.25 in 12 G) and the AZL Mariners (2 R in 2 IP). In 2019, he was 3-4 with two saves and a 3.99 ERA for the West Virginia Power, fanning 82 in 70 innings. He tied Matt De La Rosa for 7th in the South Atlantic League in games pitched (38) but was 4th with 15 hit batsmen. The 2020 minor league season was then wiped out by the COVID-19 pandemic.
Onyshko made Canada's squad for the 2020 Americas Olympic Qualifier (held in 2021 after delays due to the COVID pandemic). He made history in his debut, relieving Brendan McGuigan in the 9th with a 7-0 lead against Colombia after Andrew Albers and McGuigan had pitched no-hit ball to that point. He struck out Jesus Marriaga and walked Brayan Buelvas then Derwin Pomare hit into an error to put men on the corners and the shutout at risk. Onyshko sealed the shutout and no-hitter by striking out prospect Jeter Downs and getting Jordan Diaz on a grounder. His next outing was versus Venezuela. Relieving McGuigan with a 5-0 deficit in the 7th, one on and two out, he struck out Diego Rincones. In the 8th, he went 1-2-3 against Alexander Palma, Ramón Flores and Yonny Hernández. He led Canada in ERA in the event; Will McAffer and John Axford were also at 0.00, but in fewer innings. Canada did not qualify for the 2020 Olympics. 
His summer overall was not as good. He pitched for Everett (0-5, 2 Sv, 5.54) and the Tacoma Rainiers (9 R in 9 1/3 IP). He did strike out 75 in 46 2/3 innings but walked 25, hit 14 and threw ten wild pitches.