Go, 130 bytes

func f(r,c int)(s string){R:="<tr>"
for d,i:="<th>",0;i<r;i++{if i>0{d="<td>"}
s+=R
for j:=0;j<c;j++{s+=d+"A"}}
return"<table>"+s}

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Go, 130 123 bytes

func f(r,c int)(s string){for d,i:="<th>A",0;i<r;i++{if i>0{d="<td>A"}
s+="<tr>"
for j:=0;j<c;j++{s+=d}}
return"<table>"+s}

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• -7 bytes from removing unused variable, condensing string literals (@xigoi)