Earlier, title holder Borna Coric beat American Sebastian Korda 7-6 (5), 6-4, while another home hope Taylor Fritz survived a first-set thriller to beat Czech Jiri Lehecka 7-6 (14), 6-2.
Medvedev suffered a jarring early exit from the Canadian Masters last week but overcame some initial problems in a tricky tie against Shapovalov to edge both sets and book a meeting with American Fritz.
'We wanted to protect every player and fan after learning that Dimitrov tested positive. It was a charity event and all we wanted was to play tennis and give the fans a good show'
Borna Coric ended Roger Federer's 20-match winning streak on grass, beating him 7-6(6), 3-6, 6-2 in the Halle Open final on Sunday while also bringing to a halt the Swiss maestro's reign as World No 1.
Czech defending champion Katerina Siniakova fended off Maria Sharapova in a fiercely contested match at the Shenzhen Open on Friday to set up a final with world number one Simona Halep.