If I understand your question correctly:

You are asking for an answer in amps and giving conditions in power
and/or amps. For a resistive load.

So for a single phase resistive load and a 3 phase resistive load with
the same power consumption, the total amount of amps would be the same.
The three phase load would simply be 3 loads, each a third of the
single phase load.

For example with a single phase load of 1, the three phase load would
be three loads of 3. The same power would be dissapated(sp?) but the
current through each of the 3 phase loads would be 1/3 of the single
phase load.

With a resistive load any current shifts would not be a factor. Things
get interesting when the load is inductive and/or capacitive.

Bob AZ