A 72-year-old man with stage 4 chronic kidney disease (eGFR 23 mL/min/1.73 m²) secondary to diabetic nephropathy is reviewed in clinic. Blood pressure is 132/78 mmHg on an ACE inhibitor and a thiazide diuretic. His urine albumin-to-creatinine ratio is 80 mg/mmol. According to current Canadian recommendations, which additional medication class should be considered to slow progression of kidney disease and reduce cardiovascular risk?