Training deep learning (DL) models across Graphics Processing Unit (GPU) clusters is technically challenging. One aspect is that users have to compose command lines to adapt to the heterogeneous launchers, schedulers, affinity options, DL framework arguments, and environment variables. Composing correct command lines is error-prone and can easily frustrate users, impeding research or wasting resources. In this work, we present Maple, a multi-agent system that generates correct DL command lines with users' natural language input. Maple consists of four agents with the functionalities of information extraction, template retrieval, command line verification, and error correction. We evaluate Maple on nine GPU clusters across national computing centers in the U.S., five representative deep learning model families, and four commonly used parallel DL training paradigms. Our experiments also cover schedulers of SLURM and PBS and heterogeneous architectures, such as NVIDIA A100/H200 GPUs and Intel Max series GPUs. Maple achieves 92.0% accuracy in generating command lines across the 567 test cases. Leverage multiple language models with an aggregated size of 10B parameters, Maple delivers comparable performance to the state-of-the-art models of GPT-5, Claude, and Gemini. Together, these results highlight Maple's practical value in enabling portable and scalable distributed DL across heterogeneous HPC environments.