You don't have a CIP right? That's the most obvious card for your situation.
The CIP has a $5k MSR/3 months for 80k UR.
Will your contractor take a check or P2P payment via Venmo instead?
The CIP earns 3x UR on Plastiq (2.5% fee) and Venmo (3% fee), thus negating (and even putting you ahead of) the fee.
So for example, the contractor invoices you $3,600.
Via Plastiq, you would set up a payment to your contractor for $3,600, incur a 2.5% fee of $90, and a check is delivered to your contractor in 7-10 days. However, because payments and fees on Plastiq currently earn 3x UR when charged to the CIP, you'll earn 3x $3,690 or 11,070 UR points worth $110.70 in cash (as a statement credit or bank deposit) or $138.37 when redeemed for travel on the CSP or CIP (and as much as $166.05 if you transfer the points to a CSR and redeem them through the UR Portal).
ETA: If you're new to Plastiq and you sign up using a DISchurner link, you can earn $500 fee free dollars ("FFD") after you've made your first $500 or more payment. That means the second time you use Plastiq, they'll waive the fee on $500 of your next payment (worth $12.50).
Via Venmo, your contractor gets paid $3,600 instantly and you eat the 3% ($108) fee. However, since Venmo earns 3x UR on fees and payments when charged to the CIP, you're looking at 3x $3,708 or 11,124 UR points worth $111.24 in cash, or $139.05 in travel redeemed on a CSP/CIP, or $166.86 in travel redeemed on a CSR.
The CIP's signup bonus of 80,000 UR points is $800 in cash, or $1,000 in travel redeemed on a CSP/CIP, or $1,200 in travel redeemed on a CSR.